title: Enrollment in prescription drug insurance: the interaction of numeracy and choice set size.
abstract: OBJECTIVE
  To determine how choice set size affects decision quality among individuals of different levels of numeracy choosing prescription drug plans.
  
  
  METHODS
  Members of an Internet-enabled panel age 65 and over were randomly assigned to sets of prescription drug plans varying in size from 2 to 16 plans from which they made a hypothetical choice. They answered questions about enrollment likelihood and the costs and benefits of their choice. The measure of decision quality was enrollment likelihood among those for whom enrollment was beneficial. Enrollment likelihood by numeracy and choice set size was calculated. A model of moderated mediation was analyzed to understand the role of numeracy as a moderator of the relationship between the number of plans and the quality of the enrollment decision and the roles of the costs and benefits in mediating that relationship.
  
  
  RESULTS
  More numerate adults made better decisions than less numerate adults when choosing among a small number of alternatives but not when choice sets were larger. Choice set size had little effect on decision making of less numerate adults. Differences in decision making costs between more and less numerate adults helped explain the effect of choice set size on decision quality.
  
  
  CONCLUSIONS
  Interventions to improve decision making in the context of Medicare Part D may differentially affect lower and higher numeracy adults. The conflicting results on choice overload in the psychology literature may be explained in part by differences amongst individuals in how they respond to choice set size.
authors.affiliation: Centre for Economics and Finance, University of Porto.
authors.forename: Helena
authors.initials: H
authors.lastname: Szrek
authors.affiliation: Department of Health Research and Policy, Stanford University School of Medicine.
authors.forename: M Kate
authors.initials: MK
authors.lastname: Bundorf
mesh_terms: D000368:Aged; D002755:Choice Behavior; D005260:Female; D057220:Health Literacy / Q000706:statistics & numerical data*; D006801:Humans; D008297:Male; D008433:Mathematics; D054524:Medicare Part D / Q000191:economics; D008960:Models, Psychological; D055553:Prescription Drugs / Q000191:economics; D014481:United States
chemical_list: D055553:Prescription Drugs